1. Field of the Invention
This application relates to an electrical circuit, and in particular, to a converter circuit which is compatible with a triac based circuit.
2. Discussion of the Art
Incandescent lamps have widespread use in a variety of applications. Typically, incandescent lamps use mains or line voltage for power although in selected circumstances, low voltage is desired. For example, color rendering characteristics and light beam control are distinct advantages with low voltage lamps. Low voltage lamps, however, require a voltage lower than the line voltage because of the voltage rating of the lamp filaments. An exemplary line voltage is about 120 V, but certain lamp filaments, such as those found in MR16 lamps, have voltage ratings of only approximately 12 V. Thus, low voltage lamps require converters to reduce the line voltage to match the requirements of the lamp filament.
Although low voltage lamps have better optical light quality than high voltage lamps, the use of low voltage lamps in the business area (e.g., restaurants, commercial establishments, etc.) has not yet found widespread adoption. One reason for this may be attributed to the fact that many business establishments also desire dimmable lamps. For example, many restaurants want brighter light output during lunch hours to accommodate business lunches and want to have the capability to dim the lights during dinner hours for a more personal and private ambiance.
In order to use the low voltage lamps in traditional lamp sockets, it is known in the art to place lamps having small, integral electronic converters within existing fixtures. Typical electronic converters, however, are not readily compatible with the wide variety of commercially available triac based circuits which are prevalent in the consumer, retail, restaurant, and hotel lighting markets. Common triac based control circuits include wall dimmers and solid state switches activated by photo sensors, motion sensors, occupancy detectors, and timer controls.
Common mode chokes and resistors have been used to damp oscillations which are otherwise caused by a triac based phase dimmer circuit. While this approach provides dimming capability, it presents other problems. First, the dimensions of the outer lamp envelope constrain the size of converter circuits. Use of an inductor of 50 mH, for example, is not practical since it is a fairly large component. Additionally, the resistors compromise the efficiency of the circuit by introducing an additional (i.e., non-light producing) load to discharge the resistive-capacitive (RC) element in the dimmer circuit.
Yet another approach is to design a custom dimmable converter circuit for a low voltage lamp. This solution, however, fails to take advantage of the many available dimmer circuits already in existence. Further, if the custom design requires that the dimmer circuit be integral with the lamp, each lamp to would have to be dimmed individually. The lamp would not have the capability of being dimmed by traditional dimmer circuits, which generally have the capability control entire light fixtures, not just a single lamp. Thus, more time and labor would be required to dim the lamps, and the dimming amount may not be uniform throughout the establishment.
Accordingly, a need exists for a converter circuit compatible with commercially available triac based circuits.
A high frequency electronic power converter, which allows a low voltage lamp to be connected to standard consumer mains AC voltage through a triac based circuit, is disclosed.
An exemplary embodiment of the present invention concerns a ballast circuit operable with a triac based controller. The ballast circuit includes a rectifier configured for operative connection with an associated triac based circuit for converting AC current to DC current, a capacitor assembly coupled to the rectifier, a first connection between the rectifier and the capacitor assembly, a converter coupled to the rectifier for converting the DC current to AC current, a gate drive arrangement coupled to the converter for controlling the converter, a resistance-inductance circuit coupled to the converter, and a second connection between the capacitor assembly and the resistance-inductance circuit. The converter induces AC current in the resistance-inductance circuit.